feat: [quote] 견적 API Phase 2-3 완료 (Service + Controller Layer)

Phase 2 - Service Layer:
- QuoteService: 견적 CRUD + 상태관리 (확정/전환)
- QuoteNumberService: 견적번호 채번 (KD-{PREFIX}-YYMMDD-SEQ)
- FormulaEvaluatorService: 수식 평가 엔진 (SUM, IF, ROUND 등)
- QuoteCalculationService: 자동산출 (스크린/철재 제품)
- QuoteDocumentService: PDF 생성 및 이메일/카카오 발송

Phase 3 - Controller Layer:
- QuoteController: 16개 엔드포인트
- FormRequest 7개: Index, Store, Update, BulkDelete, Calculate, SendEmail, SendKakao
- QuoteApi.php: Swagger 문서 (12개 스키마, 16개 엔드포인트)
- routes/api.php: 16개 라우트 등록

i18n 키 추가:
- error.php: quote_not_found, formula_* 등
- message.php: quote.* 성공 메시지

app/Http/Requests/Quote/QuoteSendEmailRequest.php

@@ -0,0 +1,26 @@
+<?php
+
+namespace App\Http\Requests\Quote;
+
+use Illuminate\Foundation\Http\FormRequest;
+
+class QuoteSendEmailRequest extends FormRequest
+{
+    public function authorize(): bool
+    {
+        return true;
+    }
+
+    public function rules(): array
+    {
+        return [
+            'email' => 'nullable|email|max:100',
+            'name' => 'nullable|string|max:100',
+            'subject' => 'nullable|string|max:200',
+            'message' => 'nullable|string|max:2000',
+            'cc' => 'nullable|array',
+            'cc.*' => 'nullable|email|max:100',
+            'attach_pdf' => 'nullable|boolean',
+        ];
+    }
+}